Containers for lithography mask and method of use

ABSTRACT

A container is provided for storing a lithographic printing mask. A first container section is formed of a sturdy material which defines a central inner recess area that is shaped to house a mask and to hold outer edges of a mask without touching a pattern on the mask. A second identical container section is placed against the first container section with a mask housed within recesses of both to form a container which has a common pressure level all around and therein. A higher pressure level is then applied outside the container causes the first and second sections of the container to be held together. To remove the mask from the container, the pressure outside the container is reduced to substantially the pressure level inside the container and the first and second sections are pulled apart.

FIELD OF THE INVENTION

[0001] This invention relates to a container useful for holding(storing) mask, e.g., a Next Generation Lithography (NGL) mask, andpreventing dust or other particles from reaching the mask, and to amethod of using the container.

BACKGROUND OF THE INVENTION

[0002] Keeping a mask used in the fabrication of integrated circuitsclean is critical. Dust or other particles on a mask can causecorresponding spots to be formed on the substrate of an integratedcircuit being formed when the mask is illuminated. Such spots willproduce an inaccurate reproduction of the mask on the substrate andthereby can reduce yield.

[0003] In prior art optical projection printing systems, light isgenerally projected from a light source through a lens arrangement andthen a mask having a predetermined pattern formed thereon that is storedin a pellicle. The image projected from the mask is incident on asubstrate having a light sensitive layer, e.g., photoresist, formed on asurface thereof. In this regard, see, for example, U.S. Pat. No.4,131,363 (Shea et al.), issued on Dec. 26, 1978. The pellicle in suchprinting systems generally comprises a solid frame for holding a mask,and a transparent thin film that covers an upper opening of the frame.To print a mask pattern, the substrate and the mask within the pellicleare cleaned to remove any dust or particles thereon, and the bottom ofthe pellicle frame is securely mounted above the substrate around alight sensitive layer thereon to be irradiated. The pattern on the maskwithin the pellicle is then irradiated to transfer the pattern of themask onto the light sensitive layer on the substrate. Generally, dust orother particles on the transparent thin film stretched over the pellicleframe is of no concern. This is because the film is positioned asufficient distance above the mask so that dust or other particles onthe film are out of focus when the surface of the substrate isirradiated through the mask with the type of radiation (e.g.,Ultraviolet (UV), deep UV, or X-ray radiation) used in the prior artsystems. Therefore, such dust or other particles on the surface of thepellicle itself do not affect the printed pattern on the substrate.

[0004] Pellicles used in the prior art photolithography systems aregenerally secured to the substrate by various techniques such as usingan adhesive, vacuum chucking techniques, magnets, and spring loadingarrangements to protect the mask area from dust or other particles. Inthis regard see, for example, U.S. Pat. No. 4,833,051 (Imamura), issuedon May 23, 1989. Prior art pellicles also have included variouspassageways through the sides of the pellicle frame for equalizingatmospheric pressure changes that occur between the protected areawithin the pellicle and outside of the pellicle while still protectingthe protected area within the pellicle from dust or particles. Suchpassageway arrangements prevent the thin film covering the frame of thepellicle from deforming and contacting the surface of the mask when thepellicle is transported via different altitudes and/or environments.These passageways in the pellicle frame can include serpentine channelsor a straight through passageway with filters mounted therein. In thisregard see, for example, the Imamura patent cited above, and U.S. Pat.No. 6,055,040 (Sego), issued on Apr. 25, 2000.

[0005] For all Next Generation Lithography (NGL) systems where a narrowbeam of radiation is used as, for example, electron beam printingtechnology, keeping a mask clean is critical. However, known pelliclematerials are not transparent enough to radiation, e.g., electron beamsand extreme ultraviolet radiation, used with NGL systems.

[0006] It is desirable to provide a container for holding a mask that isto be used with NGL systems during transportation, storage, etc. to keepdust and/or particles from depositing on the mask. The design of thecontainer should also reduce the chance of dust and/or particle beingdeposited on a mask during mask loading and unloading into and out ofthe container.

SUMMARY OF THE INVENTION

[0007] The present invention is directed to a container and use thereoffor temporarily storing a Next Generation Lithography (NGL) mask inorder to keep such a mask clean prior to it being used with, forexample, electron beam printing technology.

[0008] A first apparatus aspect of the present invention is a containerfor housing a lithographic mask. The apparatus comprises a first sectionand a second section. The second section is in contact with the firstsection with the contacting first and second sections defining a cavityhaving a size which is sufficient to house a lithographic mask andprovide an air tight seal around the cavity when pressure within thecavity is less than pressure outside the container such that dust andother particles cannot reach a lithographic mask housed in the cavity.

[0009] A second apparatus aspect of the present invention is a containerfor storing a lithographic printing mask. The container comprises afirst container section formed of a sturdy material and a secondcontainer section formed of a sturdy material. When the first and secondcontainer sections are placed together they define a cavity thereinhaving a size to fixedly house a mask while not contacting a maskpattern on the mask and provide an air tight seal around the cavity whenpressure within the cavity is less than pressure outside the containersuch that dust and other particles cannot reach the mask housed in thecavity.

[0010] A third apparatus aspect of the present invention is a containerfor storing a lithographic printing mask. The container comprises firstand second sections. The first container section is formed of a sturdymaterial and defines a first cavity which is shaped for contacting anedge section of a mask to be stored in the container and covers, butdoes not contact an area of a mask pattern on the mask when the edgesection of the mask is placed in the cavity. The second containersection is formed from a sturdy material and defines a second cavitytherein having a size which contacts an edge section of a mask to bestored in the container wherein when the first and second containersections are placed together they fixedly house the mask in the firstand second cavities and provide an air tight seal around the cavity whenpressure within the first and second cavities is less than pressureoutside the container such that dust and other particles cannot reachthe mask housed in the cavity.

[0011] A fourth apparatus aspect of the present invention is a containerfor storing a lithographic printing mask.

[0012] The container comprises first and second container sections. Thefirst container section is formed of a sturdy material and defines afirst cavity which is shaped for contacting an edge section of a mask tobe stored in the container and covers, but does not contact an area of amask pattern on the mask when the edge section of the mask is placed inthe cavity. The second container section is formed from a sturdymaterial and defines a second cavity therein having a size whichcontacts an edge section of a mask to be stored in the container whereinwhen the first and second container sections are placed together theyfixedly house the mask in the first and second cavities and provide anair tight seal around the cavity when pressure within the first andsecond cavities is less than pressure outside the container such thatdust and other particles cannot reach the mask housed in the cavity.

[0013] A method aspect of the present invention is a method of storing amask in a container comprising first and second sections which are bothcleaned to remove particles thereon. The method comprising the steps of:placing first and second cleaned sections of the container and a cleanedmask in a chamber and reducing the pressure within the chamber to afirst pressure level; while the mask is in the chamber which is at thefirst pressure level, placing the mask in a cavity defined by portionsof the first container section such that a mask pattern on the mask doesnot contact any portion of the first container; while the mask is in thecavity, placing the second container section in contact with the firstcontainer section to form the container and to seal the cavity thereinfrom dust and particles and any pressure changes outside the container;and raising the first pressure level surrounding the container to asecond higher pressure level to seal and hold the first and secondcontainer sections together.

[0014] The invention will be better understood from the following moredetailed description taken with the accompanying drawing and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 shows a cross-sectional side view of a container with aNext Generation Lithography (NGL) mask stored (housed) therein inaccordance with the present invention;

[0016]FIG. 2 shows a cross-sectional schematic view of a vacuum chamberwith the container (shown in perspective view) of FIG. 1 housing a NGLmask in accordance with the present invention; and

[0017]FIG. 3 shows a cross-sectional side view of an other containerwith NGL mask stored (housed) therein in accordance with the presentinvention.

[0018] The drawings are not necessarily to scale.

DETAILED DESCRIPTION OF THE INVENTION

[0019] It is to be understood that corresponding elements having thesame function in the several views of the drawings are provided with thesame designation numbers.

[0020] Referring now to the FIG. 1, there is shown a cross-sectionalside view of a container 10 for storing (housing) a mask 12 inaccordance with the present invention. The container 10 is particularlysuited for housing (storing) a mask 12 of the type used in NextGeneration Lithography (NGL) systems including electron beam lithographyand may be used for housing conventional lithographic masks. The storagecontainer 10 comprises an upper half 14 and a lower half 16. In apreferred embodiment the halves 14 and 16 are identical. The upper half14 and the lower half 16 of the storage container 10 are formed of asturdy material such as, for example, a metal, plastic, or other sturdycomposition material (i.e., a material capable of esentially notdeforming with a vacuum applied to portions thereof). Each of the upperand lower halves 14 and 16 defines first and second inner recesssections (cavities) 18 a and 18 b in a portion of the first and secondhalves 14 and 16 when the two halves 14 and 16 are placed together. Thefirst inner recess section (cavity) 18 a is formed around an outsideedge of the overall inner recess area for contacting and holding edgeportions of the mask 12 when it is stored therein. The second innerrecess section (cavity) 18 b, which is deeper than the first innerrecess section 18 a, is in a central area of the overall inner recessarea so that it does not contact, and is over the area of the mask 12where a mask pattern is actually found. A compressible O-Ring 19 ispositioned around a surface 15 of one of the upper and lower halves 14and 16 where the halves 14 and 16 where the upper and lower halves 14and 16 come together to prevent air leakage into the first and secondinner recess section 18 a and 18 b when the container 10 is subsequentlyvacuum sealed with a mask 12 stored therein. The compressible materialcan comprise any suitable material such as, rubber, which will seal thefirst and second inner recesses 18 a and 18 b. Optionally, smallchannels (not shown) can be formed in both the upper and lowers halves14 and 16 of container 10. These channels are in communication with eachother at least one location where the upper and lower halves 14 and 16contact each other so as to help ensure that pressures in recesses 18 bof both halves are equal.

[0021] Referring now to FIG. 2, there is shown a perspective view of avacuum chamber 26 with the container 10 of FIG. 1 therein. To mount amask 12 in the container 10, the first and second halves are separatedand placed within the vacuum chamber 26 (shown within a dashed linerectangle) which is dust and particle free. A selectively operatedvacuum source (not shown) reduces the pressure in the chamber 26 to apredetermined vacuum level via a port 28. The surfaces of the mask 12and especially the inner recess areas 18 a and 18 b are then cleaned tomake sure that no dust or particles remain thereon. The mask 12 is thenplaced in the inner recess section 18 a of the second half 16 of thecontainer 10, and the first half of the container 10 is symmetricallyplaced onto the second half 16 and in contact with the O-ring 19. At hispoint in time, the predetermined pressure (vacuum) level in the chamber26 is the same inside the first and second inner recess areas 18 a and18 b and outside the container 10 The pressure in the chamber 26 is thenincreased to atmospheric pressure outside of the chamber 26. Thepressure outside the container 10 is now greater than the pressure levelinside the first and second inner recess sections 18 a and 18 b. Thisholds the first and second halves together. Additionally, the O-ring 19is compressed by the holding force of the vacuum in the first and secondinner recesses 18 a and 18 b to prevent air from leaking into the firstand second inner recess sections 18 a and 18 b. The container 10 storing(housing) a mask 12 can then be then removed from the chamber 26 andshipped to where it will be used.

[0022] In use, a container 10 housing a mask 12 is placed in a cleanchamber 26 where a lithographic machine (not shown) is located. Thepressure in the chamber 26 is reduced to the predetermined vacuum levelso that the container 10 can be opened, i.e., the sections 14 and 16 canbe separated. Once the container 10 in opened in the clean chamber 26,the mask 12 is removed from the container 10 and transferred for use inthe lithographic machine to print a plurality of circuit substrates (notshown). It is to be noted that the upper 14 and lower 16 halves are notconnected together at all by a hinge or other type of coupling device.This means that there are no surfaces that rub against each other whenthe two halves 14 and 16 are separated. Accordingly, there are noparticles formed from a coupling device that can fall onto the mask 12stored in the container 10 of FIG. 1 or the container 10 a of FIG. 2.

[0023] Referring now to FIG. 3, there is shown a cross-sectional sideview of a container 10 a for storing (housing) a mask 12 in accordancewith the present invention. The container 10 a is similar to thecontainer 10 of FIG. 1 but comprises a different outside configurationwithout extra protrusions, and has a somewhat different internal recessconfiguration. The storage container 10 a comprises an upper half 14 aand a lower half 16 a which have a rectangular shape. Each of the upperand lower halves 14 a and 16 a defines first and second inner recesssections 18 aa and 18 bb in a portion thereof when the two halves 14 aand 16 a are placed together. The first inner recess section 18 aa isformed around an outside edge of the overall inner recess area forcontacting and holding edge portions of the mask 12 when the mask 12 isstored in the upper and lower halves 14 a and 16 a. This avoids movementof the mask 12 during any movement of the container 10 a which can causethe possible release of particles from the rubbing of the mask 12 withthe container 10 a. The second inner recess section 18 bb, which isdeeper than the first inner recess section 18 aa, is in a centralportion of the overall inner recess area so that it does not contact andis over the area of the mask 12 where a mask pattern (not shown) isactually found.

[0024] A layer of a compressible material 20 is positioned around thecircumference of the container 10 a outside the first inner recesssection 18 aa where the upper and lower halves 14 a and 16 a cometogether to prevent air leakage into the first and second inner recesssection 18 aa and 18 bb when the container is subsequently vacuum sealedwith a mask 12 stored therein. The upper half 14 a and the lower half 16a of the container 10 a are formed of a sturdy material such as, forexample, a metal, plastic, or other sturdy composite material and definefirst and second inner recess sections 18 aa and 18 bb when the twohalves 14 a and 16 a are placed together. The recess section 18 aa isformed around the recess section 18 bb and is sized to hold edgeportions of the mask 12 when it is stored therein. The inner recesssection 18 aa is sized such that it does not contact the area of themask 12 where the mask pattern is actually found. The layer of acompressible material 20 is positioned around a surface 15 a of at leastone of the upper and lower halves 14 a and 16 a where the halves 14 aand 16 a come together to prevent air leakage into the first and secondinner recess sections 18 aa and 18 bb when the container 10 a issubsequently vacuum sealed with a mask 12 therein. The compressiblematerial 20 can comprise any suitable material such as, rubber, whichwill seal the first and second inner recesses 18 aa and 18 bb.

[0025] The mask 12 can be inserted and removed from container 10 a usingthe vacuum chamber 26 of FIG. 2 in essentially the same manner ascontainer 10 of FIG. 1 has a mask 12 inserted and then removedtherefrom.

[0026] It is to be appreciated and understood that the specificembodiment of the invention described hereinbefore are merelyillustrative of the general principles of the invention. Variousmodifications may be made by those skilled in the art which areconsistent with the principles set forth. More particularly, the firstand second halves 14, 14 a and 16, 16 a can have any other shape as, forexample, a rectangular outside shape with or without externalprotrusions from that shown in FIGS. 1-3.

What is claimed is:
 1. A container for housing a lithographic maskcomprising: a first section; and a second section in contact with thefirst section with the contacting first and second sections defining acavity having a size which is sufficient to house a lithographic maskand provide an air tight seal around the cavity when pressure within thecavity is less than pressure outside the container such that dust andother particles cannot reach a lithographic mask housed in the cavity.2. A container for storing a lithographic printing mask comprising: afirst container section formed of a sturdy material; and a secondcontainer section formed of a sturdy material, wherein when the firstand second container sections are placed together they define a cavitytherein having a size to fixedly house a mask while not contacting amask pattern on the mask and provide an air tight seal around the cavitywhen pressure within the cavity is less than pressure outside thecontainer such that dust and other particles cannot reach the maskhoused in the cavity.
 3. The container of claim 2 further comprising acompressible material located on a surface of at least one of the firstand second container sections where they come together and surroundingthe cavity defined by the first and second container sections forproviding the air tight seal.
 4. The container of claim 3 wherein thecompressible material is an O-ring.
 5. The container of claim 3 whereinthe compressible material is a layer of a compressible material.
 6. Thecontainer of claim 2 wherein the first and second container sections areformed from a material from one of a group consisting of metal, plastic,and a sturdy composition material.
 7. The container of claim 2 wherein aclean mask is placed in the cavity of a cleaned first container sectionin a clean vacuum chamber at a predetermined first pressure level, acleaned second container section is aligned with the first containersection and is placed in contact with the first container section, andthe first pressure level in the vacuum chamber is raised to a secondhigher pressure level to seal and hold the sealed first and secondcontainer sections together.
 8. A container for storing a lithographicprinting mask comprising: a first container section formed of a sturdymaterial and defining a first cavity which is shaped for contacting anedge section of a mask to be stored in the container and covers, butdoes not contact an area of a mask pattern on the mask when the edgesection of the mask is placed in the cavity; a second container sectionformed from a sturdy material and defining a second cavity thereinhaving a size which contacts an edge section of a mask to be stored inthe container wherein when the first and second container sections areplaced together they fixedly house the mask in the first and secondcavities and provide an air tight seal around the cavity when pressurewithin the first and second cavities is less than pressure outside thecontainer such that dust and other particles cannot reach the maskhoused in the cavity.
 9. A container for storing a lithographic printingmask comprising: a first container section formed of a sturdy materialand defining a first cavity which is shaped for contacting an edgesection of a mask to be stored in the container and covers, but does notcontact an area of a mask pattern on the mask when the edge section ofthe mask is placed in the cavity; a second container section formed froma sturdy material and defining a second cavity therein having a sizewhich contacts an edge section of a mask to be stored in the containerwherein when the first and second container sections are placed togetherthey fixedly house the mask in the first and second cavities and providean air tight seal around the cavity when pressure within the first andsecond cavities is less than pressure outside the container such thatdust and other particles cannot reach the mask housed in the cavity. 10.The container of claim 9 further comprising a compressible materiallocated on a surface of at least one of the first and second containersections where they come together and surrounding the first and secondcavities defined by the first and second container sections,respectively, for providing the air tight seal.
 11. The container ofclaim 10 wherein the compressible material is an O-ring.
 12. Thecontainer of claim 9 wherein the compressible material is a thin layerof a compressible material.
 13. The container of claim 9 wherein thefirst and second container sections are formed from a material selectedfrom a group consisting of metal, plastic, and a sturdy compositionmaterial.
 14. The container of claim 9 wherein a clean mask is placed inthe cavity of a cleaned first container section in a clean vacuumchamber at a predetermined first pressure level, a cleaned secondcontainer section is aligned with the first container section and isplaced in contact with the first container section, and the firstpressure level in the vacuum chamber is raised to second higher pressurelevel to seal and hold the sealed first and second container sectionstogether.
 15. A method of storing a mask in a container comprising firstand second sections which are both cleaned to remove particles thereon,the method comprising the steps of: placing first and second cleanedsections of the container and a cleaned mask in a chamber and reducingthe pressure within the chamber to a first pressure level; while themask is in the chamber which is at the first pressure level, placing themask in a cavity defined by portions of the first container section suchthat a mask pattern on the mask does not contact any portion of thefirst container; while the mask is in the cavity, placing the secondcontainer section in contact with the first container section to formthe container and to seal the cavity therein from dust and particles andany pressure changes outside the container; and raising the firstpressure level surrounding the container to a second higher pressurelevel to seal and hold the first and second container sections together.16. The method of claim 15 wherein a compressible material is located ona surface of at least one of the first and second container sectionswhere they come together and surrounds the cavity defined by the firstand second container sections for providing the air tight seal.
 17. Themethod of claim 16 wherein the compressible material is an O-ring. 18.The method of claim 16 wherein the compressible material is a thin layerof a compressible material.
 19. The method of claim 15 wherein the firstand second container sections are formed from a material selected from agroup consisting of metal, plastic, and any sturdy composition material.20. The method of claim 15 wherein the first pressure level is belownormal atmospheric pressure and the second pressure level is atmosphericpressure.